Add support of HIP_HIDDEN_FREE_MEM, to deduct the returned available

memory from hipMemGetInfo API, measured in MB.

Change-Id: I7a8260c12e032e04e26611db4c38c893a29f2653

src/hip_memory.cpp

@@ -1130,6 +1130,10 @@ hipError_t hipMemGetInfo  (size_t *free, size_t *total)
             hc::am_memtracker_sizeinfo(device->_acc, &deviceMemSize, &hostMemSize, &userMemSize);
 
             *free =  device->_props.totalGlobalMem - deviceMemSize;
+
+           // Deduct the amount of memory from the free memory reported from the system
+           if(HIP_HIDDEN_FREE_MEM)
+               *free -= (size_t)HIP_HIDDEN_FREE_MEM*1024*1024;
         }
         else {
              e = hipErrorInvalidValue;